Ubuntu USES Jni to develop example details
- 2020-05-12 02:33:44
- OfStack
1. Write the Java file, declare the native method in it, and load the dynamic link library through the static statement block. The sample Prompt.java code is as follows:
class Prompt {
private native String getLine(String prompt);
public static void main(String args[]) {
Prompt p = new Prompt();
String input = p.getLine("Type a line: ");
System.out.println("User typed: " + input);
}
static {
System.loadLibrary("Prompt");
}
}
2. Call javac command to generate Prompt.class file;
javac Prompt.java
3. Call the javah command to generate the Prompt.h header file for reference by the C program:
javah -jni Prompt
The automatically generated header file is as follows:
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class Prompt */
#ifndef _Included_Prompt
#define _Included_Prompt
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class: Prompt
* Method: getLine
* Signature: (Ljava/lang/String;)Ljava/lang/String;
*/
JNIEXPORT jstring JNICALL Java_Prompt_getLine
(JNIEnv *, jobject, jstring);
#ifdef __cplusplus
}
#endif
#endif
4. Wrote Prompt.c documents to achieve specific functions:
#include <jni.h>
#include <stdio.h>
#include "Prompt.h"
JNIEXPORT void JNICALL
Java_Prompt_getLine(JNIEnv *env, jobject obj, jstring prompt)
{
char buf[128];
const jbyte *str;
str = (*env)->GetStringUTFChars(env, prompt, NULL);
if(str == NULL) {
return NULL;
}
printf("%s", str);
(*env)->ReleaseStringUTFChars(env, prompt, str);
scanf("%s", buf);
return (*env)->NewStringUTF(env, buf);
}
5. Compile the dynamic library libPrompt.so;
gcc -shared -fpic -I/usr/lib/jvm/java-6-sun-1.6.0.26/include -I/usr/lib/jvm/java-6-sun-1.6.0.26/include/linux Prompt.c -o libPrompt.so
6. Run.
java Prompt
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